Anticarburizing compound



Patented Dec. 4, 1934 Lesa-11s ANTICARBURIZING COMPOUND Walter G.Wittman, Indianapolis, Ind., assignor of ten per cent to Roger F.Marshall, Indianapolis, Ind.

I lNoDrawingn, Application October 18.11933,

Serial No. 694,115 7 V I 11 Claims. (0121484) This invention relates toan anticarburizing compound which is used in the case hardening of steelproducts to localize the carburizing effect. More particularly, theinvention relates to a compound to be applied to such portions of thesurface of the product as are not to be hardened and which prevents thecarburizing of such portions.

In the case hardening process, the product to be hardened is packed in acarburizing compound *iijb and then heated to a desired temperature, atwhich temperature the carbon from the compound enters the pores of theproduct and, combining with the iron therein, makes the surfacesulficiently high in carbon content to react to a 311'5 further heattreating process for hardening. In many products, it is desirable thatonly a portion of the surface be hardened. In order to prevent thehardening of undesired parts of the surface, it has heretofore been thepractice to coat such 2% parts with an electrolytic plating of copper orother non-ferrous metal which mechanically prevents the carbon frompenetrating the surface. This method is relatively expensive, requiresconsiderable apparatus and also leaves an undesir- F i' able metalliccoating on the product.

It has also been the practice to apply other coatings, such as groundfire clay or asbestos, which mechanically prevent the access of carbonto the parts which are not to be hardened. This 1 1 31 method isdifficult of use where the products require relatively rough handling inthe packing operation since it is difficult to give the coatingsuflicient mechanical strength to resist such handling. Such coatingsalso require considerable time for drying before the product may becarburized. In certain cases, the drying time is three hours or more.

In the present invention, these objections are overcome by a coatingcompound which apparently performs its function chemically rather thanmechanically, which leaves no visible residue upon the unhardenedsurface when the carburizing process is completed and which requirespractically no drying time.

The compound forming the present invention in its most preferred formconsists in a water solution of a salt or salts of copper or a similarmetal and oxalic acid or a similar organic acid h in which there issuspended an oxide of lead. For -50 best results, I prefer to preparethe compound with the ingredients in the following proportions, I

although these proportions may be varied within a considerable range:

Parts Cupric sulphate 5 Cupric chloride 2 Oxalic acid 3 Water 5 Leadoxide 1 The proportion of ingredients given are parts by volume andrefer to a crushed crystalline form for the copper salts and the oxalicacid. The water is preferably distilled water and the lead oxide ispreferably the monoxide, litharge, PbO, in powdered form.

In the use of the compound, the solution is applied to the parts to beprotected from hardening either by dipping or by the use of a brush. Thesolution dries almost immediately, leaving the chemical ingredients ofthe compound in the form of a relatively thin coating precipitated onthe surface of the product. The coating adheres so strongly to thesurface that it can not be removed by ordinary rubbing but requiresabrasion on an emery wheel or similar tool for removal. Contrary to thecase with the mechanical coatings of the prior art, no amount of roughhandling can remove the coating. The coated product is packed in thecarburizing compound in the well known manner and heated as in the priorart. When removed from its packing, no trace of the anti-carburizingcompound is visible, although it is possible that a certain amount ofmetallic copper or lead, or both, is deposited in the pores of the iron.The parts protected by the compound are not carburized and when heatedtreated, are found to be substantially as soft as when originallyformed, while the unprotected parts are thoroughly case hardened. 90

The exact nature of the probable chemical reactions between theingredients of the compound, the carbon or carbon monoxide of thecarburizing compound and the iron is not known and no explanationthereof is attempted herein.

Where a thicker coating than usual is required, I add to the compoundone part of powdered alum. This apparently acts as a coagulator toproduce the desired thickness of coating and is useful for eiicarburizing operations longer than the ordinary.

The invention claimed is:

1. An anti-carburizing compound containing cupric chloride, oxalic acid,and a lead oxide.

2. An anti-carburizing compound containing cupric sulphate, cupricchloride, oxalic acid, and a lead oxide.

3. An anti-carburizing compound containing cupric chloride, a leadoxide, and an organic acid.

4. An anti-carburizing compound containing cupric chloride, cupricsulphate, a leadoxide, and an organic acid. I

5. An anti-carburizing compound containing cupric chloride, cupricsulphate, oxalic acid, and litharge. I

6. An anti-carburizing compound containing the following ingredients insubstantially the proportions named:

Parts Cupric sulphate 5 /2 Cupric chloride 2 Oxalic acid 3" Water 5-Lead oxide 1 '7. An anti-carburizing compound containing the followingingredients in substantially the proportions named:

Parts Cupric sulphate 5 /2 Cupric chloride 2 Oxalic acid 3 Water 5 Leadoxide 1 Powdered alum 1 8. An anti-carburizing compound containingcupric chloride, an organic acid a'lead oxide, and a coagulator.

9. An anti-carburizing compound containing cupric chloride, cupricsulphate, an organic acid, a lead oxideyand a coagulator.

